Many systems require wiring and/or electrical contacts to realize the supply of electrical power to devices. By omitting these wires and contacts the use of these devices becomes more comfortable. The use of batteries inside devices partly meets this comfort requirement, but gives a device extra weight and requires regular recharging. Power transmission via magnetic induction is a well-known method, mostly applied in transformers, but is recently refined by integrating coils into printed circuit boards (PCBs) or other flat materials, enabling wireless power transmission from a surface to a reception device. For this purpose a power supply can be equipped with a transmitter that can generate an alternating magnetic field by means of an alternating electrical current in one or more coil(s) and a mobile device can be equipped with a reception device in which an alternating electrical voltage is induced in one or more coils by this magnetic field.
To efficiently and safely provide wireless power from a power supply with multiple transmitter elements, it is necessary to detect and locate a reception device when it is near the surface of the power supply and to activate only those transmitter elements that are within the area that is covered by the reception device coil.
To further increase the efficiency and safety, transmitter and reception device communicate with each other to exchange power transfer parameters and to monitor the power transfer.
A power supply that allows multiple reception devices to be placed on its interface surface for receiving power might not have enough power to serve all placed reception devices. This could for example be the case if the power is retrieved from a USB interface, which is limited to 2.5 W. In case sufficient power is not available, the voltage of the power supply could become too low for reception devices that need a certain voltage level to charge a battery. Moreover, the time to charge a battery could become (much) longer than expected. As another example, the reduction of power for a lighting application could lead to a reduction of the light output. As a consequence, the transmission of power from a transmission device to multiple devices with the aim to efficiently and safely serve as many reception devices as possible needs to be improved.